1. Field of the Invention
The invention relates generally to methods and apparatus for machining on a relatively small scale. More particularly, the invention relates to systems for making precision cuts in small elongate objects, such as solid and tubular elements usable in invasive medical devices such as catheters and guidewires.
2. Description of Related Art
Making cuts in small solid and tubular elongate elements, for example such as wires and tubular elements used in catheters and guide wires, requires precision in order to ensure that the desired functional characteristic are achieved, and that such characteristics are achieved with reliability. However, it is also important to control costs of production.
The state of the art is typified by such devices as grinding devices for changing outer diameter of an elongate element, and by electron discharge machining (EDM) devices and laser devices for making cuts in the elongate member, and lithographic-like processes for selective removal of material. Such devices can involve relatively high cost, and in the case of lithographic processes can involve a number of separate steps. In the case of laser and EDM, machining processes, due to the nature of such devices, a finished product of less than desired quality can initially result, since heating and/or ablation of the material is involved, giving rough cut qualities and/or locally altering the material by heating, melting, thickening or thinning, so that it has less desirable properties. Also, manipulation and control systems can be a factor, as imprecise control and manipulation mechanisms for properly positioning the cutting means of the device to make the cut, as well as the elongate object to be cut, can give rise to less than desired quality of a finished product.
It has been recognized that using a micro-saw blade, such as is typically used in the microchip fabrication arts, can give superior results in cutting material in a micro-machining process. It has further been recognized that what is needed is a method and apparatus for making cuts in catheters and guide wires which allows precise control of characteristics of the cuts. This also entails precision holding, advancement and rotation of a generally elongate, and typically cylindrical, object while at least one micro-sized saw blade is advanced to make a cut to a precise depth and retracted afterward.
The invention accordingly provides a micro-machining system configured for cutting an elongate object of small transverse dimension having a lengthwise axis, comprising: a) a controller programable to enable control of cuts in the elongate object with respect to each other in terms of position along and around the lengthwise axis and to a depth desired; b) a clamp configured to enable repeatedly releasing and then holding the elongate object in a fixed position for cutting the elongate object transversely relative to the lengthwise axis; c) a pinch roller feed configured to advance the elongate element and to rotate it about a lengthwise axis of the elongate object, thereby moving the elongate object so that it can be disposed in a position for cutting; a contact reference position sensor; and, d) a cutter configured for forming the at least one precision cut in the elongate object to a desired depth into the elongate object from the sensed first contact by the cutter with the elongate object.
In another inventive aspect the system for micro-machining an elongate element having a lengthwise axis can comprise: a) a controller configured to control operation of the system, programable to produce micro-machined elongate elements of desired configurations; b) a clamp configured to engage and release the elongate element under control of the controller; c) manipulating means configured to move the elongate element along its lengthwise axis and to rotate the elongate element about its lengthwise axis under the control of the controller, further comprising an actuator controlled by the controller configured to rotate the elongate element, and an actuator controlled by the controller configured to move the element along its lengthwise axis; d) an actuator-moved saw blade configured to form cuts of small dimensions in the elongate element and to be movable toward and away from the elongate element by an actuator under control of the controller, further comprising an actuator configured to move the saw blade toward and away from the element under control of the controller, and, e) a contact reference point identification system configured to provide a signal interperatable by the controller indicating that the saw blade has approached the element and just made contact therewith without appreciable depth of cut, the system being configured to control depth of cut from a contact reference point into the elongate element by the saw blade; whereby the element can be clamped to hold it in a fixed position, and a first cut of precisely controlled depth can be made, and the element can be released and at least one of rotated and moved along and about its lengthwise axis and a second precise cut made of a desired depth in a desired position in relationship to the first cut.
In a more detailed aspect the cutter can be a rotating cutting blade forming a kerf of a small width (as used in chip manufacturing for example) that is less than 0.003 inches wide. In another more detailed aspect, the contact reference position sensor can comprise an electric circuit completed by contact between the cutter and the object. The contact reference position sensor can comprise an optical sensor which senses contact between the cutter and the object. Where the cutter is a saw blade the contact reference point identification system can comprise an electrical circuit completed by contact of the saw and the elongate element. This can be a DC circuit . This circuit can be an AC circuit. Proximity of the cutter to the elongate object can be sensed by induced current from an element of the AC circuit before contact is made.
In another more detailed aspect, movement of portions of the system with respect to each other can be facilitated by stepper motors controlled by the controller. A stepper motor under control of the controller can be configured to actuate at least one of the manipulating means and the actuator-moved saw blade. A stepper motor under control of the controller can be operatively coupled to the manipulating means to advance the elongate element, and a stepper motor under control of the controller can be operatively coupled to the manipulating means to rotate the elongate element. An actuator facilitating movement of the saw blade toward and away from the element can comprise a caliper and a stepper motor operatively connected to the caliper, configured to position the saw with respect to the element with precision, whereby a depth of cut with respect to the contact reference point can be precisely controlled.
In a further more detailed aspect, a position sensor can be provided, configured to sense movement of the blade toward and away from the element, wherein feedback control of blade position is facilitated. The sensor can be one of a LVDT and a LVDC.
In a further more detailed aspect, the system can be configured to sense at least one of a) an amount of blade wear on a cutter comprising a cutting blade; b) an asymmetry of the elongate element about its lengthwise axis at a given point along its length. The system can be configured to quantify one of an asymmetry and an out-of-round condition of the elongate element.
In another inventive aspect the system for forming cuts in a small-diameter elongate element having a lengthwise axis can comprise:
a) a controller configured to control operation of the system, programable to produce micro-machined elongate elements of desired configuration in diameter sizes usable as catheters and guidewires for invasive medical procedures in a human body;
b) a clamp configured to engage and release the elongate element under control of the controller;
c) manipulating means including a pinch roller assembly configured to grasp the elongate element, and move the elongate element along its lengthwise axis and to rotate the elongate element about its lengthwise axis under the control of the controller, further comprising an actuator comprising a stepper motor controlled by the controller configured to rotate the elongate element, and an actuator comprising a stepper motor controlled by the controller configured to move the element along its lengthwise axis;
d) an actuator-moved saw blade configured to form cuts of small dimensions in the elongate element and to be movable toward and away from the elongate element by an actuator comprising a stepper motor turning a caliper under control of the controller, wherein the actuator is configured to move the saw blade toward and away from the element under control of the controller; and,
e) a contact reference point identification system comprising an electrical circuit configured to provide a signal interperatable by the controller indicating that the saw blade has approached the element and just made contact therewith without appreciable depth of cut, the system being configured to control depth of cut from a contact reference point into the elongate element by the saw blade, whereby the element can be clamped to hold it in a fixed position, end a first cut made, then it can be released and moved by being at least one of rotated and moved along and about its lengthwise axis, and a second precise cut made to a desired depth at a desired position in relationship to the first cut.